Sixty-eight strains of Vibrio anguillarum, five of V. ordalii and the type strains of V. alginolyticus, V. carchariae, V. damsela and V. parahaemolyticus were compared using the API 20E gallery. Within the V. anguillarum strains, distinct groups could be separated mainly on the basis of their reaction on indole production and the fermentation of amygdalin and arabinose. Vibrio ordalii, the former V. anguillarum biotype 2, could easily be separated from V. anguillarum and from the other fish pathogenic Vibrio spp.